1. Technical Field
Embodiments of the invention relate to physical quantity sensors having a silicon-on-nothing (“SON”) structure, such as pressure sensors or acceleration sensors, and to manufacturing methods thereof.
2. Related Art
FIG. 7 is a schematic view of the whole of a general pressure sensor 600. The pressure sensor 600 includes a package 80, a semiconductor chip 85 fixed in a depressed portion 80a inside the package 80, an external lead-out terminal 81, which is one portion of the package 80, that connects the semiconductor chip 85 and an external circuit (not shown) via a bonding wire 82, and a gel 83 that covers the semiconductor chip 85. Also, the semiconductor chip 85 and package 80 are fixed together with an adhesive 84. Pressure (a measured pressure F) of a fluid, or the like, is applied to the semiconductor chip 85 via the gel 83, and pressure measurement is carried out.
Also, according to JP-T-2002-530641 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application) and JP-A-63-122925, a groove is formed in the periphery of a diaphragm, thereby controlling the transmission of stress to the diaphragm.
Also, in JP-A-7-20917, a recess is formed in a frame that supports a circular diaphragm 1, and an extraction portion 7 is provided as a depression from the recess to an end portion of the frame. A ring-like sealing groove having a cut in an extraction portion is provided as a depression in the upper surface of the frame in an outer peripheral region of a recess 6. A sealing portion whose upper end surface is higher than the frame is formed of a fluorine system resin, or the like, in the sealing groove and extraction portion. A cover 3 is placed on the upper surface of the frame, and bonded using an anodic bonding method, thereby creating a pressure sensor. A connecting wire provided on the inner surface of the cover is buried in the sealing portion, and the sealing portion and cover are crimped together with no gap. It is described how, by so doing, it is possible to increase the air tightness of the pressure chamber. In this invention, the sealing groove formed in the periphery of the diaphragm is formed in a ring.
Also, in JP-A-7-280679, a thin portion is integrally formed across a thick portion in the periphery of a diaphragm of a sensor element of a semiconductor of silicon, or the like, so as to encircle the diaphragm. A leg portion of the sensor element is formed on an outer side of the thin portion, and the leg portion is bonded to an attachment surface to which the sensor element is attached. It is described how, by so doing, stress from the leg portion concentrates in the thin portion, without being transmitted to the diaphragm, and it is possible to provide a highly accurate pressure sensor.
Also, in Japanese Patent No. 3,629,185, it is described how, by forming a reference pressure chamber at the same time as forming a pressure detecting portion, such as a diaphragm, in a semiconductor substrate surface, using an SON structure, it is possible to realize a semiconductor sensor that can measure with high accuracy, and a manufacturing method thereof, wherein mechanical strength is high, and it is possible to simplify the manufacturing process and reduce the cost.
Also, in JP-T-2004-531882, there is proposed a method of manufacturing a micromachine sensor, and a sensor manufactured using the method, wherein a plurality of apertures are provided in a semiconductor substrate. It is described that a heat treatment is carried out after the apertures are provided in the semiconductor substrate, and because of the heat treatment, a pressure sensor is formed of a SON structure wherein the aperture to a hollow chamber provided in a deep portion of the substrate is caused to shift.
Also, in JP-A-2009-264905, it is described that in a pressure sensor in which a bump is formed, a cavity is formed in a region corresponding to the bump in order to relax stress.
However, in JP-T-2002-530641, JP-A-7-20917, JP-A-63-122925, and JP-A-7-280679, the diaphragm is not formed in an SON structure. Also, in Japanese Patent No. 3,629,185 and JP-T-2004-531882, no stress relaxation region is formed in an outer peripheral portion of the SON structure. Furthermore, in JP-A-2009-264905, mechanical stress from a bump formed on a second SON structure is transmitted to the diaphragm, meaning that the second SON structure functions little as a stress relaxation region.
In JP-T-2002-530641, JP-A-7-20917, JP-A-63-122925, JP-A-7-280679, Japanese Patent No. 3,629,185, JP-T-2004-531882, and JP-A-2009-264905, there is no description of increasing the accuracy of a pressure sensor by forming the diaphragm in an SON structure, and providing a trench groove or SON structure that forms a stress relaxation region in an outer peripheral portion of the diaphragm.